There are several existing techniques to separate gas, such as vapor, air and/or any other gas, from fuel dispensed from a fuel dispensing unit, such as a petrol pump, to a vehicle. This separation is important since a person purchasing the fuel shall pay only for the fuel dispensed and not for any gas entrained therein. Hence it is vital to measure accurately the volume of dispensed liquid, but if the fuel is contaminated with gas, a fuel flow meter, which cannot differentiate between the liquid and the gas, will produce an erroneous reading for the volume of fuel dispensed.
To avoid erroneous readings gas is separated from fuel by means of gas separation. If too much gas is separated, the dispensing unit is stopped and fuel is prevented from being dispensed. After a stop it is common that some kind of reset maneuver must be performed before fuel may be dispensed again.
Entrained gas often forms in the fuel when it is pumped or transported along the fuel line from the main tank to the nozzle of the fuel dispensing unit. Some of the reasons for gas formation may be wake caused by moving parts such as pumps, vortexes and regions of low pressure along the fluid pathway, any unattended leakage etc. Authorities in many countries stipulate rules of accuracy for gas separation devices and issue approvals before such a device can be used in a fuel dispensing unit. Hence efficient testing and verification of a gas separator must be possible.
Another aspect is gas contamination in the form of bubbles having different volumes along the fuel line due to different pressure zones in the fuel line.
A general problem with existing devices for gas separation and means for detecting the presence of gas is that they are relatively complicated and expensive both in respect of construction and production. Another problem is that gas is not separated efficiently enough from the fuel, and yet another that the separated gas is not detected so that dispensing of fuel can be stopped. T his causes operational disturbance and increases the cost of operation. A customer also pays for gas entrained within the fuel.
EP 0 492 400 discloses a gas separator for liquid fuels comprising a feed pump, an outlet valve, a smoothing chamber and a gas separator nozzle which opens to a diffuser. A bell shaped displacement body is arranged above the diffuser and dips a constant distance into the fuel in a float chamber. When gas free liquid is fed through the diffuser, a pilot valve is open allowing the outlet valve to be open and thus fuel to be fed to a vehicle. When gas contaminated fuel is fed, the bell shaped body entrains the gas, rises and closes the pilot valve which in turn results in closure of the outlet valve.
A problem associated with the technique above is that the entrained gas must exceed a certain amount in the bell before the bell rises, resulting in a slow response time and an increased risk of feeding gas contaminated fuel to a vehicle.
U.S. Pat. No. 5,501,246 describes a device for separating gas entrained in a flow of liquid fuel. The device has a main housing with a liquid inlet, a liquid outlet and a separation chamber within the housing and between the inlet and the outlet. Gas entrained in the liquid is separated when the liquid passes within the separation chamber and the gas exits the chamber via a vent passage. Gas detection means are arranged to detect gas in the vent passage which means is connected to a pilot valve which closes when gas is detected. Closure of the pilot valve results in closure of a main valve that must be open when fuel is to be dispensed.
One problem of the device above is that it is based on hydraulic principles. This gives a slow response time and may cause gas contaminated fuel to be dispensed. Another problem is the need for two valves which both have membranes. This results in increased costs, in particular in respect of production of the device.
In summary, prior art has the problem of high costs in the form of operational down-time, necessary maintenance and service work. The units are based on mechanical and hydraulic principles which involve a high material and assembly cost. Furthermore, the response time is long from the moment when gas is detected until the dispensing of fuel is stopped. Another problem is that the techniques do not allow, for example, the pump to be stopped, but merely a valve to be closed. Yet another problem is that the techniques only have an “on-off” position, meaning that it is not possible to detect small amounts of gas that does not necessary result in closure of the main valves; the main valve is either open or closed.